Most x-ray generating devices operate in similar fashion. X-rays are produced in a vacuum tube housing or “tube” where electrons are emitted, accelerated, and then deposited upon a material of a particular composition. This process takes place, for example, within a grounded rotating anode x-ray tube comprising a vacuum, a cathode, and an anode. The cathode, when heated by an electrical current supplied by a high voltage, emits a stream of electrons. Due to an electrical potential difference across the anode and the cathode, the electrons are accelerated and impinge upon the anode, thus producing the x-rays upon impact.
Since the initial clinical use of diagnostic, general purpose medical x-ray tubes, the high voltage applied to the tube housing generally has been applied equally to each end of the tube. This “bipolar” design excludes low voltage tubes such as mammography and x-ray diffraction tubes, which generally operate at 50 kV or less.
A bipolar, two HV cable, design has become accepted to reduce the insulation requirements to ground by one half. The total voltages applied to x-ray tubes can be very high, e.g., 150 kV. It was much easier, especially in the beginning, to insulate for 75 kV positive and 75 kV negative, on opposite ends of the x-ray tube, rather than 150 kV on just one end. End-grounded x-ray tubes themselves have certain known advantages, especially cooling, and reduced off focus radiation when metal enclosed, but the x-ray tube itself is not the subject of this application.
This bipolar voltage design was first used with so-called “aerial” systems (i.e., exposed high voltage) and carried on with later “shockproof cable” systems, as cable insulation in the latter was generally natural rubber and very difficult to manufacture for 150 kV with adequate flexibility.
The continuing requirement for two cables, when used with a lead-shielded rotating anode x-ray tube, led to a generally round or pipe shaped x-ray tube enclosure for use with the oil filled “shock proof” system. The HV cable ports were placed tangentially to the circular dimension at either end, and therefore at an approximate 90° angle to the longitudinal or rotational axis of the x-ray tube (hereinafter “tube axis”). See Applicant's FIGS. 1A, 1B, 1C. This is the usual design today.
This mechanical configuration is of no consequence when the tube is mounted “overhead” on a telescoping tube or in an x-ray fluoroscopy table. It gives a reasonably compact unit, and cables leaving the tube at 90° to the longitudinal axis are acceptable.
However, attempts to improve this packaging aspect in situations where the cables caused external mechanical interference were tried, in particular, by Picker X-Ray in the 1950's. Picker's configuration (see FIGS. 2A, 2B, 2C, 2D) had the high voltage cable housings or cable ports take a 90° turn, while the plugs were disposed in opposite directions parallel to the main housing. The center portion remained as described previously (i.e., a pipe shape). This provided a minimal improvement and was shortly abandoned. Nonetheless, it shows an attempt to solve the spatial problems of conventional cable exits 90° to the tube axis. That problematic conventional cabling can interfere with optimal equipment configuration or “packaging” of the tube housings and cable exit ports in compact equipment, especially on C-arm x-ray machines (“C-arms”).
Picker, and the former Machlett Laboratories (an x-ray tube unit of Raytheon), had also experimented in the 1930's-1940's with a bipolar tube housing where the two cable sockets were placed side-by-side generally behind the rotational axis of the x-ray tube's anode (hereinafter “anode rotation axis”). The “front” of the tube was the exit point where the beam came out through a window. (See the “Dynamax Fluoro Tube” illustrated in FIGS. 3A, 3B, 3C, 3D.) This configuration had the disadvantage of increasing the housing dimension to the back, as measured along an extension of the x-ray beam axis.
Such an increase poses a major problem for a modern application to a C-arm x-ray machine: the back of the tube would hit the floor that much sooner, as the overall object is to maximize the distance between a patient on a table and an x-ray focal spot, with the x-ray source underneath the table. If the plugs were moved to the sides, to be in the plane of the center of the x-ray tube (i.e., an obvious design change), the width of the housing would become excessive, and the housing would begin to look again like FIGS. 2A-2D. The large housing would strike external objects sooner than a plain cylinder or pipe shape, especially when the whole assembly was tilted in either axis in clinical use.
Accordingly, it is a primary object of this invention to reduce the overall size of the rotating anode x-ray tube housing to avoid the housing striking external objects.
It is another primary object to provide a smaller x-ray tube housing that is ideal for use in a C-arm x-ray machine, where the x-ray tube is an extension of the C-arm without projections from the side.
It is a more specific object to provide an x-ray tube housing, commensurate with the above-listed objects, which also allows the known advantages of end grounded rotating anode tubes to be implemented on C-arms or on overhead x-ray telescopes, while eliminating one high voltage cable.
It is yet another specific object to provide an x-ray tube housing, commensurate with the above-listed objects, that is simple in design yet more reliable in use.